lib: radix-tree: native accounting of exceptional entries
The way the page cache is sneaking shadow entries of evicted pages into
the radix tree past the node entry accounting and tracking them manually
in the upper bits of node->count is fraught with problems.
These shadow entries are marked in the tree as exceptional entries,
which are a native concept to the radix tree. Maintain an explicit
counter of exceptional entries in the radix tree node. Subsequent
patches will switch shadow entry tracking over to that counter.
DAX and shmem are the other users of exceptional entries. Since slot
replacements that change the entry type from regular to exceptional must
now be accounted, introduce a __radix_tree_replace() function that does
replacement and accounting, and switch DAX and shmem over.
The increase in radix tree node size is temporary. A followup patch
switches the shadow tracking to this new scheme and we'll no longer need
the upper bits in node->count and shrink that back to one byte.
Link: http://lkml.kernel.org/r/20161117192945.GA23430@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <mawilcox@linuxonhyperv.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 8e6d552..7885796 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -220,10 +220,10 @@
{
unsigned long i;
- pr_debug("radix node: %p offset %d tags %lx %lx %lx shift %d count %d parent %p\n",
+ pr_debug("radix node: %p offset %d tags %lx %lx %lx shift %d count %d exceptional %d parent %p\n",
node, node->offset,
node->tags[0][0], node->tags[1][0], node->tags[2][0],
- node->shift, node->count, node->parent);
+ node->shift, node->count, node->exceptional, node->parent);
for (i = 0; i < RADIX_TREE_MAP_SIZE; i++) {
unsigned long first = index | (i << node->shift);
@@ -522,8 +522,13 @@
node->offset = 0;
node->count = 1;
node->parent = NULL;
- if (radix_tree_is_internal_node(slot))
+ if (radix_tree_is_internal_node(slot)) {
entry_to_node(slot)->parent = node;
+ } else {
+ /* Moving an exceptional root->rnode to a node */
+ if (radix_tree_exceptional_entry(slot))
+ node->exceptional = 1;
+ }
node->slots[0] = slot;
slot = node_to_entry(node);
rcu_assign_pointer(root->rnode, slot);
@@ -649,6 +654,8 @@
if (node) {
unsigned offset = get_slot_offset(node, slot);
node->count++;
+ if (radix_tree_exceptional_entry(item))
+ node->exceptional++;
BUG_ON(tag_get(node, 0, offset));
BUG_ON(tag_get(node, 1, offset));
BUG_ON(tag_get(node, 2, offset));
@@ -747,6 +754,37 @@
EXPORT_SYMBOL(radix_tree_lookup);
/**
+ * __radix_tree_replace - replace item in a slot
+ * @root: radix tree root
+ * @node: pointer to tree node
+ * @slot: pointer to slot in @node
+ * @item: new item to store in the slot.
+ *
+ * For use with __radix_tree_lookup(). Caller must hold tree write locked
+ * across slot lookup and replacement.
+ */
+void __radix_tree_replace(struct radix_tree_root *root,
+ struct radix_tree_node *node,
+ void **slot, void *item)
+{
+ void *old = rcu_dereference_raw(*slot);
+ int exceptional;
+
+ WARN_ON_ONCE(radix_tree_is_internal_node(item));
+ WARN_ON_ONCE(!!item - !!old);
+
+ exceptional = !!radix_tree_exceptional_entry(item) -
+ !!radix_tree_exceptional_entry(old);
+
+ WARN_ON_ONCE(exceptional && !node && slot != (void **)&root->rnode);
+
+ if (node)
+ node->exceptional += exceptional;
+
+ rcu_assign_pointer(*slot, item);
+}
+
+/**
* radix_tree_tag_set - set a tag on a radix tree node
* @root: radix tree root
* @index: index key
@@ -1561,6 +1599,8 @@
delete_sibling_entries(node, node_to_entry(slot), offset);
node->slots[offset] = NULL;
node->count--;
+ if (radix_tree_exceptional_entry(entry))
+ node->exceptional--;
__radix_tree_delete_node(root, node);